1. Field of the Invention
The present invention relates to an angular velocity detecting apparatus used in navigation systems, posture control, etc. of automobiles and, more particularly, to an angular velocity detecting apparatus of a vibration type.
2. Related Background Art
As a conventionally known vibration type angular velocity detecting apparatus there is the vibration type angular velocity detecting apparatus that makes use of occurrence of new vibration according to angular velocity of rotation because of Coriolis' force appearing on the occasion of rotating a vibrating body. An example of the angular velocity detecting apparatus of this type is a rotational velocity sensor, for example, as described in Japanese Laid-open Patent Application No. Hei 7-55479. A vibrator used in this rotational velocity sensor has the structure in which, in the XY plane, two excitation branches project in the positive Y direction from one edge of a rectangular frame and two pickup branches project in the direction of -Y from the opposite edge of the frame. In this structure, when the excitation branches are excited to vibrate in the X-directions, the excitation branches also vibrate in the Z-directions because of the Coriolis' force appearing with rotation of the vibrator and this vibration in the Z-directions is transmitted to the pickup branches. On the pickup branch side, this Z-directional vibration transmitted is detected and the angular velocity of rotation of the vibrator is derived from the detection result.
In the rotational velocity sensor of this type, however, though the excitation branches are excited to vibrate in the X-directions, part of the vibrational energy is converted to Z-directional vibration, so as to bring about leak vibration in the Z-directions. This leak vibration is also transmitted to the pickup branches as the Z-directional vibration based on the Coriolis' force was. Namely, Z-directional vibration as resultant vibration of the leak vibration and the vibration based on the Coriolis' force is transmitted to the pickup branches.
The amplitude of this leak vibration is far greater than that of the Z-directional vibration based on the Coriolis' force, so that the leak vibration can be big noise against the vibration based on the Coriolis' force. There is, however, a shift of 90.degree. between phases of the leak vibration and the vibration based on the Coriolis' force, and the Z-directional vibrations both can be detected independently of each other.
Such Z-directional vibrations of the excitation branches and pickup branches are of mutually opposite phases with respect to the fulcrum at the central part of the frame, irrespective of either the leak vibration or the vibration based on the Coriolis' force. Specifically, when the excitation branches are deflected upward or in the positive Z direction, the pickup branches are deflected downward or in the negative Z direction.
Since the conventional, rotational velocity sensor described above is constructed without any consideration to a vibrational balance between the excitation branches and the pickup branches as to such Z-directional vibrations, the frame constituting the fulcrum of the both branches swings in the Z-directions according to the vibration of the both branches. This swing impedes transmission of the Z-directional vibration from the excitation branches to the pickup branches, so as to degrade detection accuracy of vibration at the pickup branches. Particularly, when excitation phases of the two excitation branches are reverse, a twist takes place in the frame, so that the degradation of detection accuracy becomes much greater.